collapse cross-account dupes, Lato UI font, mail-list selection & density tuning

Backend:
- Collapse identical cross-account deliveries in a thread: new messages.delivery_id
  (migration 0011) preserves the real Message-ID even when message_id_hdr is
  synthesized (§7.1); get_thread groups by it and reports also_in_account_ids; the
  list count counts distinct deliveries. Backfill script for existing rows.

Frontend:
- Bundle Lato (SIL OFL) as the UI font; unread mail-list rows use Black weight.
- Mail-list selection: hover-avatar checkbox, tri-state "select all", bulk
  Archive/Pin/Delete (Restore/Delete in Archive/Trash/Spam) with a count in the
  reading pane; unread blue dot; "also delivered to" note in the thread.
- Spacing/size tuning: sender-column width, icon gaps, avatar size, bar heights,
  and a round of -1px font sizes across the sidebar, mail list, and reading pane.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U72FZiF1W1pb8XxyWBTREA

frontend/src/components/thread/ThreadView.tsx

@@ -188,7 +188,7 @@ function ActionsMenu({
         onClick={() => setOpen((v) => !v)}
       >
         {t("mail.actions")}
-        <span className="text-[9px]">▾</span>
+        <span className="text-[11px]">▾</span>
       </button>
       {open && (
         <div className="absolute right-0 z-20 mt-1 w-52 overflow-hidden rounded-md border border-app-border bg-app-elevated py-1 shadow-lg">
@@ -215,6 +215,7 @@ function MessageItem({
   zIndex,
   showReplyBar,
   canReply,
+  alsoIn,
   onToggle,
   onReply,
   onToggleRead,
@@ -231,6 +232,7 @@ function MessageItem({
   zIndex: number;
   showReplyBar: boolean;
   canReply: boolean;
+  alsoIn: string[];
   onToggle: () => void;
   onReply: (kind: string) => void;
   onToggleRead: () => void;
@@ -286,9 +288,9 @@ function MessageItem({
           onClick={onToggle}
         >
           {avatar()}
-          <span className="min-w-0 flex-1 truncate text-sm">
+          <span className="min-w-0 flex-1 truncate text-[15px]">
             {senderName}
-            <span className="ml-2 text-app-faint">{message.snippet}</span>
+            <span className="ml-2 text-xs text-app-faint">{message.snippet}</span>
           </span>
           <span className="shrink-0 text-xs text-app-faint">{fmtRelative(message.date)}</span>
         </button>
@@ -302,7 +304,7 @@ function MessageItem({
                 className="flex w-full items-baseline justify-between gap-2 text-left"
                 onClick={onToggle}
               >
-                <span className="min-w-0 truncate text-sm">
+                <span className="min-w-0 truncate text-[15px]">
                   {senderName}
                   {message.from_addr[0]?.email && (
                     <span className="text-app-faint"> &lt;{message.from_addr[0].email}&gt;</span>
@@ -320,7 +322,7 @@ function MessageItem({
                   <span className="truncate">
                     {t("mail.to")} {recipientSummary(message.to_addr)}
                   </span>
-                  <span className="text-[9px] text-app-faint">{showDetails ? "▲" : "▼"}</span>
+                  <span className="text-[11px] text-app-faint">{showDetails ? "▲" : "▼"}</span>
                 </button>
                 <div className="flex shrink-0 items-center gap-3 text-xs">
                   {location && <span className="font-semibold text-app-fg">{location}</span>}
@@ -355,6 +357,11 @@ function MessageItem({
                   />
                 </div>
               </div>
+              {alsoIn.length > 0 && (
+                <div className="mt-0.5 truncate text-xs text-app-faint">
+                  {t("mail.alsoIn")} {alsoIn.join(", ")}
+                </div>
+              )}
               {showDetails && (
                 <dl className="mt-2 grid grid-cols-[auto_1fr] gap-x-3 gap-y-0.5 border-t border-app-border pt-2 text-xs text-app-muted">
                   <dt className="text-app-faint">{t("mail.from")}</dt>
@@ -514,8 +521,8 @@ export function ThreadView({
 
   return (
     <div data-testid="thread-view" className="flex h-full flex-col overflow-y-auto bg-app-bg">
-      <div className="sticky top-0 z-10 flex h-[44px] shrink-0 items-center justify-between gap-2 border-b border-app-border bg-app-surface px-4">
-        <h2 className="truncate text-base font-semibold text-app-fg">{subject || "(no subject)"}</h2>
+      <div className="sticky top-0 z-10 flex h-[52px] shrink-0 items-center justify-between gap-2 border-b border-app-border bg-app-surface px-4">
+        <h2 className="truncate text-[17px] font-semibold text-app-fg">{subject || "(no subject)"}</h2>
         <div className="flex shrink-0 items-center gap-1">
           <button
             className="rounded p-1.5 text-app-muted hover:bg-app-hover hover:text-app-fg"
@@ -558,6 +565,9 @@ export function ThreadView({
           }`;
           // Reply/Reply-all/Forward make no sense on a trashed message.
           const canReply = specialUse.get(message.mailbox_id) !== "trash";
+          const alsoIn = (message.also_in_account_ids ?? [])
+            .map((id) => accounts?.find((a) => a.id === id)?.email)
+            .filter((e): e is string => Boolean(e));
           return (
             <Fragment key={message.id}>
               <MessageItem
@@ -570,6 +580,7 @@ export function ThreadView({
                 zIndex={z}
                 showReplyBar={isNewest && composing?.anchorId !== message.id}
                 canReply={canReply}
+                alsoIn={alsoIn}
                 onToggle={() => toggle(message.id)}
                 onReply={(kind) => openReply(message, kind)}
                 onToggleRead={() => toggleRead(message)}